The disclosed technology relates to reduction of turbo sludge formation in the course of lubricating a turbo-charged, sump-lubricated internal combustion engine which is susceptible to contamination of lubricant with liquid fuel.
Modern engine lubricants are formulated to provide performance in a number of important areas. One of these areas is the minimization of sludge and related deposits in the engine. Problems with excessive sludge formation have historically been associated with extensive stop-and-go driving particularly during cold, damp weather conditions. Sludge formation in the crankcase and oils passages of an engine can seriously limit the ability of the crankcase oil to lubricate the engine effectively. To address this problem, most engine lubricants contain dispersants such as succinimide dispersants of various types, and these have usually been quite effective at retaining sludge-forming materials in solution or dispersion. An example of the use of a succinimide dispersant to address problems of sludge is reported in U.S. Pat. No. 6,770,605, Stachew et al., Aug. 3, 2004.
Recently, however, new sludge problems have appeared. Sludge and deposits have been observed, especially in turbo-chargedengines, and in particular turbo-charged gasoline (spark-ignited) engines, for instance, on the cylinder head and in the lubricant sump. This heavy sludge and deposit formation may lead to bearing oil starvation and blockage of the oil feed filter and, in extreme cases, to catastrophic engine failure. These problems seem more severe in engines that are fueled with certain grades of gasoline. This “turbo sludge” problem has been resistant to solution by the customary use of dispersants.
Lubricants for internal combustion engines, including those equipped with turbochargers, are known. For example, U.S. Pat. No. 6,458,750, Dardin et al., Oct. 1, 2002, discloses an engine oil composition with reduced deposit-formation tendency, including an alkyl alkoxylate. Deposit formation is evaluated in terms of, among other things, turbo deposition in heavy diesel engines. U.S. Pat. No. 6,586,276, Nakanishi et al., Jul. 1, 2003, discloses a heat resistant and oxidation resistant lubricating oil composition which includes a polyphenylthioether as an antioxidant or a lubricating base oil component. A heat resistant base oil may be used. The lubricant is suitable for automobile engines such as turbo engines, and jet engines and gas turbines operated at high speed and high temperature. U.S. Patent Application Publication US 2003/0162674, Scott, Aug. 28, 2003, discloses a heavy duty diesel engine lubricating oil comprising a Group III basestock, a detergent composition, and one or more other additives. The lubricant is said to minimize the loss of efficiency of a turbo-charger included in the engine assembly.
It is believed that the prior art does not recognize the unique difficulties associated with turbo sludge nor does it provide a way to minimize the turbo sludge.